The invention relates to a vehicle roof having a light transmissive cover formed of at least one outer panel, and a device for altering the light transmissibility of the cover.
When the following description refers to alteration of the light transmissibility, this means altering the amount of light that normally penetrates the panel, or the panels, of a light transmissive cover into the vehicle interior, based on the materials used therefor, inclusive of possibly applied coatings. This maximum, in connection with the percentage values given here, corresponds to a reference value of 100%.
It is known to interiorly provide transparent covers of sliding roofs and/or lifting roofs of vehicles with mechanically activated devices for the purpose of changing the light transmissibility. To this end, either extractable, spring-loaded shutters are employed for simple lifting roofs, or, in connection with sliding roofs, or sliding and lifting roofs, individually displaceable liner parts of non-transparent material are used beneath such roofs. These known devices have various drawbacks.
One common drawback is a relatively large construction height in comparison to the thickness of the transparent component, due to the necessary additional components required for guiding and housing such a device. An additional drawback of sliding liners, in connection with light-transmissive covers that are extended above the vehicle roof surface, is that, while they block off the incoming solar rays when closed, they, simultaneously, impair the ventilating effect of the extended cover.
Moreover, such liners and shutters have the drawback that darkening can only occur progressively in the movement direction, so that darkening in steps is only possible when it affects the entire surface of the light transmissive component; and it is not possible with respect to partial areas. Additionally, in connection with lifting roofs, so far, the only known shutters are those that are completely open or completely closed.
Furthermore, it is known to integrate devices into light-transmissive components for altering the light transmissibility, which, for this purpose, are acted upon by external energy. In this connection, mention should be made of multi-layered glass panels having an enclosed liquid crystal layer (Published German Application DE 38 17 946 A1) whose transparency can be changed depending upon an applied voltage. French Patent 1,574,762 describes two panels which are resiliently disposed with respect to each other, and depending upon the pressure of a fluid pressure source providing an intermediate liquid film of variable thickness, an inherently variable transparency is obtainable.
While the construction height of such integrated devices is low, they are not cost-effective in their construction and installation into a vehicle, due to the necessary coupling to the respective energy source.